Method of manufacturing disk substrate, and method and device for manufacturing optical disk

ABSTRACT

A method for producing a disk-shaped substrate  10  used for producing an optical disk includes: (a) forming a protective layer  12   a  that is larger in area than the disk-shaped substrate  10  on a surface of a transparent plate  11   a ; and (b) cutting a portion of the plate  11   a  with the protective layer  12   a  formed thereon other than an outer edge portion of the protective layer  12   a  to form a disk shape. According to this producing method, a thin substrate can be prevented from being damaged by forming a protective layer. Furthermore, according to this producing method, a protective layer with a uniform thickness can be formed.

TECHNICAL FIELD

[0001] The present invention relates to a method for producing adisk-shaped substrate, a method for producing an optical disk and anapparatus for producing an optical disk

BACKGROUND ART

[0002] Optical disks are spreading widely as information recording mediafor reproducing or recording information using laser light. Opticaldisks can be classified as a read-only type, a write-once type and arewritable type. Examples of the read-only optical disks include compactdisks and laser disks. Write-once or rewritable optical disks are usedas information recording media. Some of these optical disks have aconfiguration in which an information layer is formed on one principalplane of a transparent substrate (thickness: 1.2 mm) and a protectivefilm is formed thereon.

[0003] In recent years, a digital versatile disk (DVD) that is anoptical disk with a large capacity has been commercialized. Inrecording/reproducing of a high-density optical disk such as a DVD,laser light with a short wavelength and an objective lens with a largenumerical aperture (NA) are used. More specifically, laser light with awavelength of 650 nm and an objective lens with a NA of 0.60 are used.The thickness of a substrate on a light-incident side of a DVD is 0.6mm. When using one resin substrate having a thickness of 0.6 mm, themechanical strength is low and tilt occurs, so that a DVD is formed byattaching two substrates to each other with information recordingsurfaces placed inside. Herein, the term “tilt” refers to an inclinationbetween an optical axis of laser light incident upon an optical disk forrecording/reproducing and a normal line to an information recordingsurface of the optical disk.

[0004] In order to increase further the density of information to berecorded onto an optical disk, the use of a blue purple laser lightsource (wavelength: about 400 nm) also is proposed. In this case, thethickness of a transparent resin layer from the surface of a substrateto a reflective layer is set to be about 0.1 mm, and a fine laser spotis formed by using a lens with a NA of about 0.85, whereby a signal isrecorded/reproduced. However, a decrease in the wavelength of laserlight and an increase in a NA of the objective lens decrease anacceptable value of tilt. In order to increase the acceptable value oftilt, it is effective to decrease the thickness of the resin layer on alight-incident side.

[0005] As a method for producing an optical disk in which a resin layeron a light-incident side is thin (e.g., 0.1 mm), a signal recordinglayer is formed on a substrate with a thickness of 1.1 mm, and a thinresin sheet is attached to the signal recording layer or the signalrecording layer is coated with UV-curable resin. There also is a methodin which, after the signal recording layer is formed on the thin resinsheet, the resin sheet and the thick substrate are attached to eachother.

[0006] The present invention relates to an optical disk that is formedby attaching two substrates to each other. More specifically, the objectof the present invention is to provide a novel method for producing adisk-shaped substrate for use in production of an optical disk, a novelmethod for producing an optical disk and a novel apparatus for producingan optical disk.

DISCLOSURE OF INVENTION

[0007] In order to achieve the above-mentioned object, a method forproducing a disk-shaped substrate of the present invention is used forproducing an optical disk, including the processes of:

[0008] (a) forming a protective layer that is larger in area than thedisk-shaped substrate on a surface of a transparent plate; and

[0009] (b) cutting a portion of the plate with the protective layerformed thereon other than an outer edge portion of the protective layerto form a disk shape. According to this producing method, a thinsubstrate can be prevented from being damaged by forming a protectivelayer. Furthermore, according to this producing method, a protectivelayer with a uniform thickness can be formed.

[0010] According to the above-mentioned method for producing asubstrate, a thickness of the plate may be in a range of 0.03 mm to 0.3mm. According to this configuration, in particular, an optical diskcapable of performing high-density recording can be obtained.

[0011] According to the above-mentioned method for producing asubstrate, the protective layer may be made of radiation-curable resin.In the present specification, “radiation” is intended to include all ofthe electromagnetic waves and particle waves, for example, UV-light andan electron beam. The radiation-curable resin refers to resin that iscured by irradiation with these radiations.

[0012] According to the above-mentioned method for producing asubstrate, the plate may have a disk shape with a diameter larger thanthat of the disk-shaped substrate. According to this configuration, aplate can be handled easily.

[0013] According to the above-mentioned method for producing asubstrate, the process (a) may include coating the plate with theradiation-curable resin by spin coating, and curing theradiation-curable resin. According to this configuration, in particular,a disk-shaped substrate can be produced easily.

[0014] According to the above-mentioned method for producing asubstrate, the protective layer may be made of a material with ahardness higher than that of the plate. According to this configuration,a substrate can be prevented from being damaged.

[0015] According to the above-mentioned method for producing asubstrate, the protective layer may be made of a material with acoefficient of friction smaller than that of the plate. According tothis configuration, since heat is unlikely to be generated even if apickup head and a substrate come into contact with each other, thesubstrate can be prevented from being damaged.

[0016] According to the above-mentioned method for producing asubstrate, the protective layer may be made of an inorganic substance,and the protective layer may be formed by chemical vapor deposition inthe process (a). According to this configuration, a protective layerwith a uniform thickness can be formed on a thin plate with a largearea.

[0017] According to the above-mentioned method for producing asubstrate, the process (a) further may include forming an inorganiclayer made of an inorganic substance on the protective layer. Accordingto this configuration, in particular, a substrate can be prevented frombeing damaged by using a protective layer with a high hardness and aninorganic layer with a small coefficient of friction.

[0018] Furthermore, a first producing method of the present invention isa method for producing an optical disk including a first substrate and asecond substrate that is thinner than the first substrate, including theprocesses of:

[0019] (A) forming a protective film on one principal plane of thesecond substrate; and

[0020] (B) attaching the first substrate and the second substrate toeach other so that the protective film is placed outside. According tothe conventional producing method, there is a problem in that thesurface of a second substrate to be a light incident side is likely tobe damaged in the course of production or use. However, according to thefirst producing method of the present invention, the surface of asubstrate on a light incident side can be prevented from being damaged.

[0021] According to the above-mentioned first producing method, thethickness of the second substrate may be in a range of 0.03 mm to 0.3mm. According to this configuration, in particular, an optical diskcapable of performing high-density recording can be produced.

[0022] The above-mentioned first producing method further may includethe process of (C) removing the protective film from the secondsubstrate after the process (B).

[0023] According to the above-mentioned first producing method, theprocess (A) may include forming a signal recording layer on the otherprincipal plane opposed to the one principal plane after forming theprotective film.

[0024] According to the above-mentioned first producing method, thefirst substrate and the second substrate may be attached to each otherusing radiation-curable resin in the process (B). According to thisconfiguration, in particular, production becomes easy.

[0025] According to the above-mentioned first producing method, theprotective film may have a flexural rigidity smaller than that of thesecond substrate.

[0026] According to the above-mentioned first producing method, theprotective film may have a hardness higher than that of the secondsubstrate or have a flexural rigidity larger than that of the secondsubstrate. According to this configuration, a second substrate can behandled easily.

[0027] According to the above-mentioned first producing method, a firstcentral hole may be formed in the first substrate, a second central holemay be formed in the second substrate, and the second central hole maybe larger than the first central hole.

[0028] According to the above-mentioned first producing method, thesecond central hole may be larger than a clamp region. In the presentspecification, a “clamp region” refers to a region held for rotating anoptical disk when the optical disk is used.

[0029] According to the above-mentioned first producing method, athickness of the protective film may be 30 μm or more.

[0030] The above-mentioned first producing method further may includethe processes of:

[0031] (a) forming the protective layer that is larger in area than thesecond substrate on a surface of a transparent plate; and

[0032] (b) cutting a portion of the plate with the protective layerformed thereon other than an outer edge portion of the protective layerto form the second substrate, before the process (A). According to theabove-mentioned configuration, a second substrate can be prevented frombeing damaged by forming a protective layer with a uniform thickness.

[0033] According to the above-mentioned first producing method, athickness of the plate may be in a range of 0.03 mm to 0.3 mm.

[0034] According to the above-mentioned first producing method, theplate may have a disk shape with a diameter larger than that of thesubstrate.

[0035] According to the above-mentioned first producing method, theprotective layer may be made of radiation-curable resin, and the process(a) may include coating the plate with the radiation-curable resin byspin coating, and curing the radiation-curable resin.

[0036] According to the above-mentioned first producing method, theprotective layer may be made of a material with a hardness higher thanthat of the plate.

[0037] According to the above-mentioned first producing method, theprotective layer may be made of a material with a coefficient offriction smaller than that of the plate.

[0038] Furthermore, a second producing method of the present inventionis a method for producing an optical disk including a first substrateand a second substrate in which a signal area is to be formed on oneprincipal plane, including the processes of:

[0039] (i) fixing the other principal plane of the second substrate,which is an opposite side of the one principal plane, to a support;

[0040] (ii) forming at least one film selected from a metal film, adielectric film, a magnetic film and a coloring film on the oneprincipal plane;

[0041] (iii) attaching the first substrate and the second substrate toeach other with the at least one film interposed therebetween; and

[0042] (iv) releasing the other principal plane of the second substratefrom the support. According to the conventional producing method, thereis a problem in that a warp and a wave may be caused in a secondsubstrate when a metal film or the like is formed on the secondsubstrate. In contrast, according to the second producing method of thepresent invention, an optical disk with less warp and wave can beproduced easily. In the present specification, a “signal region” refersto a region where an information signal is recorded, and in this region,pits corresponding to an information signal, address pits for recordingaddress information, or grooves for tracking servo control, a reflectivefilm and the like are formed. Furthermore, a film made of a materialthat is changed in phase by irradiation with light, a magnetic film, adielectric film, or the like is formed in the signal region, inaccordance with a method for recording an information signal.

[0043] According to the above-mentioned second producing method, thethickness of the second substrate may be in a range of 0.03 mm to 0.3mm.

[0044] According to the above-mentioned second producing method, thefirst substrate may include a signal area on one principal plane on aside that is attached to the second substrate. According to thisconfiguration, an optical disk having a two-layered signal recordinglayer can be produced.

[0045] According to the above-mentioned second producing method, thefirst substrate and the second substrate may be attached to each otherusing radiation-curable resin in the process (iii).

[0046] According to the above-mentioned second producing method, thesupport and the second substrate may have radiation permeability, andthe first substrate and the second substrate may be attached to eachother by curing the radiation-curable resin by radiation from thesupport side in the process (iii). According to this configuration, evenin the case where a first substrate has no radiation permeability, thefirst substrate and the second substrate can be attached to each other,and in particular, an optical disk having a two-layered signal recordinglayer can be produced easily.

[0047] The above-mentioned second producing method may include formingthe signal area on the one principal plane of the second substrate afterthe process (i) and before the process (ii). According to thisconfiguration, the signal region can be formed while the secondsubstrate is kept flat, and pits or grooves for the signal region can beformed stably.

[0048] According to the above-mentioned second producing method, thesecond substrate may have a circular through-hole at a center thereof,and the process (i) may include pressing at least one selected from aninner peripheral edge and an outer peripheral edge of the secondsubstrate to the support side by a pressure member, thereby fixing theother principal plane to the support.

[0049] Furthermore, a first producing apparatus of the present inventionis an apparatus for producing an optical disk using a first substrateand a second substrate, including: attachment means for attaching thefirst substrate and the second substrate with a protective film formedon one principal plane to each other so that the protective film isplaced outside; and peeling means for peeling the protective film.According to this producing apparatus, the first producing method of thepresent invention for producing an optical disk can be conducted easily.

[0050] The above-mentioned first producing apparatus further may includefilm-forming means for forming the protective film on the one principalplane of the second substrate.

[0051] In the above-mentioned first producing apparatus, the attachmentmeans may include: coating means for coating at least one substrateselected from the first substrate and the second substrate withradiation-curable resin; stacking means for stacking the first substrateand the second substrate so that a center of the first substrate ismatched with a center of the second substrate; and irradiation means forirradiating the radiation-curable resin with radiation.

[0052] In the above-mentioned first producing apparatus, the attachmentmeans further may include rotation means for rotating the stacked firstsubstrate and second substrate.

[0053] In the above-mentioned first producing apparatus, the coatingmeans may include dropping means for dropping the radiation-curableresin onto the at least one substrate and rotation means for rotatingthe at least one substrate, and the stacking means may include acontainer that can be evacuated.

[0054] Furthermore, a second producing apparatus of the presentinvention is an apparatus for producing an optical disk including afirst substrate and a second substrate in which a signal area is to beformed on one principal plane, including:

[0055] a support for supporting the other principal plane of the secondsubstrate, which is an opposite side of the one principal plane; and

[0056] fixing means for fixing the other principal plane to the support.

[0057] According to the second producing apparatus, the second producingmethod of the present invention for producing an optical disk can beconducted easily.

[0058] The above-mentioned second producing apparatus further mayinclude film-forming means for forming at least one film selected from ametal film, a dielectric film, a magnetic film and a coloring film onthe one principal plane.

[0059] The above-mentioned second producing apparatus further mayinclude attachment means for attaching the first substrate and thesecond substrate to each other.

[0060] In the above-mentioned second producing apparatus, the supportmay be made of a radiation-permeable material, and the attachment meansincludes irradiation means on a side opposite to a side where the secondsubstrate is placed with respect to the support.

[0061] In the above-mentioned second producing apparatus, the secondsubstrate may have a circular through-hole at a center thereof, and thefixing means may include pressure means for pressing at least oneselected from an inner peripheral edge and an outer peripheral edge ofthe second substrate to the support side.

[0062] The second producing apparatus further may include signal areaforming means for forming the signal area on the one principal plane ofthe second substrate.

BRIEF DESCRIPTION OF DRAWINGS

[0063]FIG. 1A is a plan view of a disk-shaped substrate produced by aproducing method of the present invention. FIG. 1B is a centralcross-sectional view of FIG. 1A.

[0064]FIGS. 2A and 2B are cross-sectional views illustrating an exampleof processes of a method for producing a disk-shaped substrate accordingto the present invention.

[0065]FIGS. 3A and 3B are cross-sectional views showing another exampleof processes of a method for producing a disk-shaped substrate accordingto the present invention.

[0066]FIGS. 4A to 4C are still another example of processes of a methodfor producing a disk-shaped substrate according to the presentinvention.

[0067]FIG. 5 is a cross-sectional view showing the state of one processof the producing method in FIG. 4.

[0068]FIG. 6 is a cross-sectional view illustrating one process of amethod for producing a disk-shaped substrate of the present invention.

[0069]FIGS. 7A to 7D are cross-sectional views illustrating stillanother example of a method for producing a disk-shaped substrate of thepresent invention.

[0070]FIGS. 8A to 8D are cross-sectional views illustrating an exampleof processes of a method for producing an optical disk of the presentinvention.

[0071]FIGS. 9A to 9C are cross-sectional views illustrating anotherexample of a method for producing an optical disk of the presentinvention.

[0072]FIGS. 10A to 10E are cross-sectional views illustrating stillanother example of a method for producing an optical disk of the presentinvention.

[0073]FIGS. 11A to 11C are cross-sectional views illustrating stillanother example of a method for producing an optical disk of the presentinvention.

[0074]FIGS. 12A to 12C are cross-sectional views illustrating stillanother example of a method for producing an optical disk of the presentinvention.

[0075]FIGS. 13A to 13D are cross-sectional views illustrating stillanother example of a method for producing an optical disk of the presentinvention.

[0076]FIGS. 14A and 14B are plan views showing an example of a substrateused for a method for producing an optical disk of the presentinvention.

[0077]FIG. 15 is a schematic view showing an example of an apparatus forproducing an optical disk of the present invention.

[0078]FIGS. 16A and 16B are schematic cross-sectional views showing anexample of fixing means for a second substrate in the apparatus forproducing an optical disk of the present invention.

[0079]FIGS. 17A and 17B are schematic cross-sectional views showing anexample of constituent components of an apparatus for producing anoptical disk of the present invention.

[0080]FIGS. 18A and 18B are schematic views illustrating an example ofprocesses of a method for producing an optical disk using the apparatusfor producing an optical disk of the present invention.

[0081]FIGS. 19A and 19B are schematic views showing a function of anexample of constituent components of the apparatus for producing anoptical disk of the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0082] Hereinafter, the present invention will be described by way ofembodiments with reference to the drawings. In the followingdescription, like parts will be denoted with like reference numerals,and a repeated description thereof may be omitted.

[0083] Embodiment 1

[0084] In Embodiment 1, an example of a method for producing adisk-shaped substrate used in the production of an optical disk will bedescribed.

[0085] First, FIG. 1A shows a plan view of a disk-shaped substrate 10produced by the producing method, and FIG. 1B shows a centralcross-sectional view thereof. Referring to FIGS. 1A and 1B, thesubstrate 10 includes a substrate 11 and a protective layer 12 formed onthe substrate 11. A through-hole may be formed at the center of thesubstrate 10. Furthermore, an inorganic layer made of an inorganicsubstance may be formed on the protective layer 12.

[0086] The substrate 11 is made of plastic or the like. Morespecifically, the substrate 11 can be made of polycarbonate, acrylicresin, norbornene resin, olefin resin, vinyl ester resin, or the like.The thickness of the substrate 11 is, for example, in a range of 0.03 mmto 0.3 mm.

[0087] The protective layer 12 is formed for the purpose of preventingthe substrate 11 from being damaged when an information signal isrecorded/reproduced using an optical pickup head or when the substrate11 is handled. In order to prevent the substrate 11 from being damaged,it is preferable that the protective layer 12 is formed of a materialwith a hardness higher than that of the substrate 11 or a material witha coefficient of friction with respect to a pickup head smaller thanthat of the substrate 11. As a material for the protective layer 12,radiation-curable resin or an inorganic substance such as diamond-likecarbon can be used. As the radiation-curable resin, for example, a hardcoat material (e.g., Dyecure SD-715 produced by Dainippon Ink andChemicals, Inc.) with a hardness higher than that of polycarbonate, orUV-curable resin (e.g., acrylic resin) having a pencil hardness of H ormore can be used. In the case where the protective layer 12 is made ofradiation-curable resin, the thickness of the protective layer 12 is,for example, in a range of 0.1 μm to 30 μm. Furthermore, the protectivelayer 12 may be formed of a thermosetting material. As the thermosettingmaterial, siloxane resin or vinyl ester resin can be used.

[0088] In the case where the substrate 11 cannot be protectedsufficiently only with the protective layer 12, an inorganic layer witha small coefficient of friction may be formed on the protective layer12, as described below. For example, it may be possible that theprotective layer 12 is formed of a hard coat material with a highhardness, and a diamond-like carbon layer with a small coefficient offriction is formed thereon.

[0089] Hereinafter, FIGS. 2A and 2B show cross-sectional viewsillustrating processes of a producing method of Embodiment 1. Accordingto the producing method of Embodiment 1, as shown in FIG. 2A, aprotective layer 12 a is formed on the surface of a transparent plate 11a (Process (a)). The transparent plate 11 a is to be the substrate 11 bycutting, and is larger in area than the substrate 11. The protectivelayer 12 a is to be the protective layer 12 by cutting, and is larger inarea than the substrate 11. The plate 11 a and the protective layer 12 arespectively are made of the same materials as those of the substrate 11and the protective layer 12. Furthermore, the plate 11 a and theprotective layer 12 a respectively have the same thicknesses as those ofthe substrate 11 and the protective layer 12. In the case where theprotective layer 12 a is made of radiation-curable resin, the protectivelayer 12 a can be formed by a method described later. Furthermore, inthe case where the protective layer 12 a is made of an inorganicsubstance, for example, the protective layer 12 a can be formed bychemical vapor deposition (CVD), sputtering, or vapor deposition.

[0090] Next, in the plate 11 a with the protective layer 12 a formedthereon, a portion of the plate 11 a other than that corresponding to anouter edge portion of the protective layer 12 a is cut to form a diskshape (Process (b)). The portion other than that corresponding to anouter edge portion of the protective layer 12 a refers to a portion awayfrom an outer peripheral edge of the protective layer 12 a by 1 mm ormore (preferably 3 mm or more). The plate 11 a can be cut by punchingwith a die or blowout using laser light or an electric arc. In the caseof using a die, a method using a Thomson blade or a method in accordancewith a shearing system can be used. In this process, as shown in FIG.2B, the substrate 10 including the substrate 11 and the protective layer12 formed on the surface of the substrate 11 can be produced. In theprocess (b), a through-hole may be formed at the center of the substrate10.

[0091] The process (a) may include the process of forming an inorganiclayer 13 a made of an inorganic substance on the surface of theprotective layer 12 a, as shown in FIG. 3A. The inorganic layer 13 a canbe made of diamond-like carbon or SiO₂, for example. The inorganic layer13 a can be formed by CVD or sputtering. In this case, as shown in FIG.3B, a substrate 10 a in which the inorganic layer 13 is formed on theprotective layer 12 can be produced by cutting the plate 11 a. Theinorganic layer 13 may be formed after cutting the plate 11 a.

[0092] Hereinafter, the producing method will be described specificallyby way of two examples. A first specific example will be described withreference to FIGS. 4A to 4C.

FIRST EXAMPLE

[0093] In the first example, the protective layer 12 is formed ofradiation-curable resin. First, as shown in FIG. 4A, radiation-curableresin 42 a (represented by hatching) before being cured is dropped ontoa transparent plate 41 a (example of the plate 11 a) through a nozzle43. In this process, while the resin 42 a is being dropped, the plate 41a is moved in a longitudinal direction, and the nozzle 43 is swung in awidth direction of the plate 41 a. The nozzle 43 is swung so that itsswing becomes a half or more of the width of the plate 41 a. Due to thisswinging, the resin 42 a can be disposed over the surface of the plate41 a. Polycarbonate with a thickness of 85 μm can be used as the plate41 a. Furthermore, the above-mentioned hard coat material can be used asthe resin 42 a.

[0094] The dropped resin 42 a is spread to a substantially uniformthickness by a squeegee 44 placed in the vicinity of the nozzle 43,whereby a layer 45 is formed. The squeegee 44 is a spatula made of aflat plate having predetermined stiffness. The spacing between thesqueegee 44 and the plate 41 a is set in accordance with the thickness(e.g., 5 μm) of the protective layer to be formed. Thus, by moving theplate 41 a, the layer 45 made of the resin 42 a before being cured canbe formed to a substantially uniform thickness.

[0095]FIG. 5 shows a cross-sectional view in a width direction of theplate 41 a with the layer 45 formed thereon. The direction perpendicularto the drawing surface of FIG. 5 corresponds to a longitudinal directionof the plate 41 a. As shown in FIG. 5, the layer 45 becomes thick at theend of the plate 41 a due to surface tension. Therefore, the layer 45includes a portion 45 a with a substantially uniform thickness and athick portion 45 b.

[0096] Next, as shown in FIG. 4B, the layer 45 is irradiated withradiation 46 such as an electron beam or UV-light to cure theradiation-curable resin, thereby forming a protective layer 47 a. Theradiation 46 may be radiated continuously or in a pulse manner (thisalso applies to the irradiation of radiation described below). In orderto prevent the thickness of the protective layer 47 a from being varied,it is preferable that the radiation 46 is radiated immediately after thelayer 45 is formed with the squeegee 44. The protective layer 47 a hasthe same shape as that of the layer 45 shown in FIG. 5.

[0097] Next, as shown in FIG. 4C, the plate 41 a with the protectivelayer 47 a (example of the protective layer 12 a) formed thereon ispunched with a die 48, whereby a disk-shaped substrate 49 (example ofthe substrate 10; thickness: 90 μm, for example) is obtained. In thecase where a central hole is formed in the substrate 49, the die 48preferably has two blades corresponding to an inner periphery and anouter periphery of the substrate 49. For example, the substrate 49 isobtained by using a die having a Thomson blade in an annular shapecorresponding to an inner periphery and an outer periphery of thesubstrate 49.

[0098] In the first example, the layer 45 may be formed by anothermethod. For example, a method for spraying the resin 42 a to the plate41 a and a method for soaking the plate 41 a in the resin 42 a can beused. In the case of spraying the resin 42 a, a nozzle for spraying theresin 42 a may be used as the nozzle 43. In the case where the layer 45with a substantially uniform thickness can be formed by spraying theresin 42 a, the squeegee 44 may be omitted.

[0099]FIG. 6 shows a method for forming the layer 45 by soaking.According to this method, the plate 41 a is soaked in the resin 42 aplaced in a container 61. The plate 41 a pulled up from the resin 42 ais irradiated with radiation to cure the resin 42 a, whereby aprotective layer can be formed. At this time, one surface of the plate41 a is masked, whereby a protective layer can be formed only on theother surface of the plate 41 a. It also may be possible that thethickness of the resin layer is made uniform with a squeegee in the sameway as in FIG. 4A immediately after the plate 41 a is pulled up from theresin 42 a.

SECOND EXAMPLE

[0100] Next, a second specific example of the producing method ofEmbodiment 1 will be described with reference to FIGS. 7A to 7D.According to the second method, a disk-shaped plate is used as the plate11 a. First, as shown in FIG. 7A, a plate 71 is punched with a die 72 toform a disk-shaped transparent plate 71 a. The plate 71 a has a diameterlarger than that of a substrate 75 to be formed finally. As the die 72,the same die as that described in the first method can be used. At thistime, a central hole may be formed simultaneously. Furthermore, theplate 71 a may be formed by casting or injection molding.

[0101] Next, as shown in FIG. 7B, while the disk-shaped plate 71 a isrotated slowly, the radiation-curable resin 42 a before being cured isdropped through the nozzle 43. The resin 42 a is the same as thatdescribed in the first example.

[0102] Next, as shown in FIG. 7C, by rotating the plate 71 a at a highspeed, a resin layer with a substantially uniform thickness is formed.Furthermore, by irradiating the resin layer with radiation, the resinlayer is cured to form a protective layer (corresponding to theprotective layer 12 a). The protective layer thus formed has a largerthickness at an outer peripheral portion, and has a substantiallyuniform thickness at a portion other than the outer peripheral portion.

[0103] Finally, as shown in FIG. 7D, by punching the plate 71 a with adie 74, the substrate 75 (corresponding to the substrate 10) with theprotective layer 73 formed thereon can be obtained. The die 74corresponds to the shape of the substrate 75. In this process, a centralhole may be formed. According to the second method, the substrate 75also is formed by punching out the portion where the thickness of theprotective layer is substantially uniform, so that a substrate with aprotective layer having a uniform thickness formed thereon can beobtained.

[0104] According to the producing method of Embodiment 1, care should betaken for the following two points. The first point is that a regionwhere the protective layer 12 a has a uniform thickness is identified,and an area for forming the protective layer 12 a is determined so thatthe region becomes larger than that of the substrate 11. The secondpoint is that a region where the protective layer 12 a has a uniformthickness is cut out to form the substrate 10.

[0105] In Embodiment 1, the case where the protective layers 12 and 12 aare made of radiation-curable resin has been described. However, theselayers may be formed of thermosetting resin.

[0106] Furthermore, according to the producing method of Embodiment 1,as the plate 11 a, it may be possible to use a substrate with a signalarea formed on a surface opposite to a surface where the protectivelayer 12 a is formed. In the signal area, unevenness corresponding to aninformation signal and grooves for tracking are formed. In this case, itis required to cut out the substrate 11 from the plate 11 a so that thesignal area is positioned appropriately in the substrate 11.Furthermore, in this case, a recording film or a reflective film may beformed on a surface of the plate 11 a or the substrate 11 where thesignal area is formed. Furthermore, the signal area may be formed beforeforming the substrate 11 (before punching out the substrate 11) or maybe formed after forming the substrate 11. The signal area can be formed,for example, by a photopolymer method.

[0107] Furthermore, although the method for producing a circulardisk-shaped substrate has been described in Embodiment 1, the producingmethod is not limited to a circular disk-shaped substrate and isapplicable to production of a rectangular or polygonal card-shapedrecording medium.

[0108] Embodiment 2

[0109] In Embodiment 2, an example of a producing method of the presentinvention for producing an optical disk will be described. Thisproducing method is a method for producing an optical disk having afirst substrate and a second substrate thinner than the first substrate.FIGS. 8A to 8D show cross-sectional views illustrating processes of theproducing method of Embodiment 2.

[0110] First, as shown in FIG. 8A, a second substrate 82 is prepared.The second substrate 82 is made of plastic or the like. Morespecifically, the second substrate 82 can be formed of polycarbonate,acrylic resin, norbornene resin, olefin resin, vinyl ester resin, or thelike. The thickness of the second substrate 82 is, for example, in arange of 0.03 mm to 0.3 mm, for example, 0.05 mm, 0.1 mm, or 0.2 mm. Acentral hole 82 h is formed in the second substrate 82. The diameter ofthe central hole 82 h preferably is larger than that of a clamp regiondescribed later. The central hole 82 h may be formed after the firstsubstrate and the second substrate are attached to each other.Furthermore, a signal area may be formed on one principal plane 82 bopposed to one principal plane 82 a.

[0111] Next, as shown in FIG. 8B, a protective film 83 is formed on oneprincipal plane 82 a of the second substrate 82 (Process (A)). Theprotective film 83 is formed for the purpose of preventing the surfaceof the second substrate 82 from being damaged when the second substrate82 is handled so as to produce an optical disk. It is preferable thatthe protective film 83 has a flexural rigidity lower than that of thesecond substrate 82 or has a hardness higher than that of the secondsubstrate 82. The thickness of the protective film 83 is, for example,in a range of 0.03 mm to 1.2 mm. By prescribing the thickness of theprotective film 83 to be 30 μm or more, the second substrate 82 can beprotected sufficiently. By prescribing the total of the thickness of thesecond substrate 82 and the thickness of the protective film 83 in arange of 0.5 mm to 0.7 mm, a conventional producing apparatus used forproducing an optical disk can be used.

[0112] In the case where the protective film 83 is removed in a laterprocess, the protective film 83 is formed of a material that is likelyto be removed from the second substrate 82, or the second substrate 82and the protective film 83 are attached to each other with weakadhesion. For example, the protective film 83 may be formed oflight-curable resin with weak adhesion to the second substrate 82.Furthermore, the second substrate 82 and the protective film 83 may beattached to each other with an adhesive or by static electricity.Furthermore, it also may be possible that the surface of the protectivefilm 83 is made rough to some degree, and the second substrate 82 andthe protective film 83 are attached to each other by applying pressure.In the case where the protective film 83 is not removed in a laterprocess, the protective film 83 is formed of a material that is unlikelyto peel off the second substrate 82.

[0113] Next, as shown in FIG. 8C, the first substrate 81 and the secondsubstrate 82 are attached to each other so that the protective film 83is placed outside (Process (B)). More specifically, one principal plane81 a of the first substrate 81 is attached to one principal plane 82 bof the second substrate 82. A signal area may be formed on one principalplane 81 a of the first substrate 81. Furthermore, a signal recordinglayer is formed respectively on one principal plane 81 a and oneprincipal plane 82 b, whereby an optical disk having two signalrecording layers can be produced.

[0114] The first substrate 81 and the second substrate 82 can beattached to each other with radiation-curable resin. The first substrate81 can be formed of the same material as that of the second substrate82. The first substrate 81 is thicker than the second substrate 82. Thetotal of the thickness of the first substrate 81 and the secondsubstrate 82 preferably is in a range of 0.5 mm to 0.7 mm, or in a rangeof 1.1 mm to 1.3 mm. In this range, a conventional producing apparatusused for producing an optical disk can be used. Furthermore, byprescribing the total of the thicknesses of two substrates in a range of1.1 mm to 1.3 mm, compatibility with respect to a conventional opticaldisk can be ensured. A central hole 81 h may be formed in the firstsubstrate 81. The central hole 81 h may be formed after the firstsubstrate 81 and the second substrate 82 are attached to each other.

[0115] Thus, an optical disk having the first substrate 81 and thesecond substrate 82 can be produced. The producing method of Embodiment2 further may include a process (Process (C)) of removing the protectivefilm 83 from the second substrate 82, as shown in FIG. 8D. Theprotective film 83 can be removed by the method described below.

[0116] Hereinafter, the producing method of Embodiment 2 will bedescribed by way of 6 specific examples.

FIRST EXAMPLE

[0117]FIG. 9 shows a cross-sectional view illustrating processes of thefirst example. First, as shown in FIG. 9A, a disk-shaped first substrate91 and a disk-shaped second substrate 92 are prepared. The firstsubstrate 91 is made of polycarbonate formed by injection molding. Thefirst substrate 91 has a thickness of 1.1 mm, a diameter of 120 mm, anda diameter of a central hole 91 a of 15 mm. Pits corresponding to aninformation signal are formed on one principal plane 91 a of the firstsubstrate 91. Furthermore, a reflective film (not shown) made ofaluminum with a thickness of 100 nm is formed on one principal plane 91a. The pits and the reflective film on one principal plane 91 a form asignal area. The reflective film can be formed by sputtering.

[0118] The second substrate 92 is made of polycarbonate or acrylicresin. The second substrate 92 can be formed by a method for cutting asheet formed by casting, or injection molding. The second substrate 92has a thickness of 90 μm, a diameter of 120 mm and a diameter of acentral hole 92 h of 15 mm. A signal area is not formed on the secondsubstrate 92. The surface of the second substrate 92 is flat. Aprotective film 94 made of polyester resin is formed on one principalplane of the second substrate 92. A central hole 94 h is formed in theprotective film 94. The protective film 94 has a thickness of 60 μm, adiameter of 120 mm and a diameter of a central hole 94 h of 15 mm. Theprotective film 94 can be formed by a method for extruding a materialthrough a slit, injection molding, or casting. The second substrate 92and the protective film 94 can be attached to each other withlight-curable resin having weak adhesion, an adhesive, or staticelectricity. Furthermore, it also may be possible that the surface ofthe protective film 94 is made rough to some degree, and the secondsubstrate 92 and the protective film 94 are attached to each other byapplying pressure.

[0119] Next, as shown in FIG. 9B, one principal plane 91 a of the firstsubstrate 91 and the second substrate 92 are attached to each other sothat the protective film 94 is placed outside. An attachment method willbe described with reference to FIG. 10.

[0120] First, as shown in FIG. 10A, the first substrate 91 is placed ona table 101, and light-curable resin 103 is dropped onto one principalplane 91 a of the first substrate 91 through a nozzle 102. The resin 103is placed in an annular shape with a diameter of about 54 mm. At thistime, the first substrate 91 or the nozzle 102 is rotated at a low speedof 20 rpm to 120 rpm. The resin 103 may be applied to the secondsubstrate 92.

[0121] Next, as shown in FIG. 10B, the second substrate 92 is stacked onthe first substrate 91 so that the first substrate 91 and the secondsubstrate 92 are placed concentrically, and the protective film 94 isplaced outside. More specifically, the first substrate 91 is fixed tothe table 101 with a pin 104. Then, the second substrate 92 is moved bybeing held by an arm 105, and the central hole of the second substrate92 is fitted on the pin 104. According to the producing method ofEmbodiment 2, since the protective film 94 is held by the arm 105, evenif the second substrate 92 is thin, the second substrate 92 can beprevented from being damaged.

[0122] Next, as shown in FIG. 10C, the first substrate 91 and the secondsubstrate 92 are rotated at a high speed (e.g., 1000 rpm to 10000 rpm)by rotating the table 101, whereby the resin 103 is spread to an outerperipheral edge of the substrate. According to this method, air bubblescan be prevented from being mixed between the first substrate 91 and thesecond substrate 92, and excessive resin 103 can be discharged.

[0123] Next, as shown in FIG. 10D, light 106 such as UV-light isradiated to cure the resin 103. At this time, the light 106 may beradiated from an upper side, from a lower side, or from both the upperand lower sides. In the case where the light 106 is radiated from thelower side, a radiation-transmitting table such as glass is used. Thelight 106 may be radiated in a pulse manner or continuously. By varyingthese radiation conditions, the tilt (inclination) of an optical diskcan be controlled.

[0124] Next, the protective film 94 is peeled off the second substrate92. FIG. 10E shows an enlarged view in the vicinity of the central holeduring this process. Specifically, a part of an inner peripheral edge ofthe protective film 94 is floated with a hook 107, and an air stream 108is blown to the floated inner peripheral edge, whereby the protectivefilm 94 is peeled off. Thereafter, the protective film 94 is removedwith an adsorption arm. In the process shown in FIG. 10C, the resin 103may be transferred to the protective film 94 side of the secondsubstrate 92. However, the protective film 94 can prevent the resin 103from adhering to the surface of the second substrate 92. The peeledprotective film 94 can be reused as it is, or reused after melting.

[0125] Thus, an optical disk can be produced. In the first example, thecase where the first substrate 91 is fixed to the table 101 has beendescribed. However, the second substrate 92 may be fixed to the table101. Even in this case, the side of the second substrate 92 on which theprotective film 94 is formed is fixed to the table 101, so that thesurface of the second substrate 92 can be prevented from being damagedwhen the table 101 is rotated.

[0126] Furthermore, in the first example, a signal area is formed onlyon the first substrate 91. However, a semi-transparent signal area maybe formed even on the second substrate 92. In this case, if a signalarea is formed directly on the second substrate 92, it is not easy toform the signal area on the thin second substrate 92 by sputtering.However, by forming a protective film with a high stiffness on thesecond substrate 92, it becomes easy to form a signal area on the secondsubstrate 92.

[0127] Furthermore, in the first example, the case where a read-onlyoptical disk is produced has been described. However, according to theproducing method of Embodiment 2, an optical disk in which aninformation signal can be written also can be produced.

SECOND EXAMPLE

[0128] In the second example, the case will be described in which thediameter of the central hole 92 h of the second substrate 92 and that ofthe central hole 94 h of the protective film 94 are varied in the firstexample. The description of the same components as those in the firstexample will be omitted here.

[0129] In the second example, as shown in FIG. 11A, the central holes 92h and 94 h are made larger than the central hole 91 h of the firstsubstrate 91. More specifically, the diameters of the central holes 92 hand 94 h are set to be 40 mm. In this configuration, the secondsubstrate 92 is not placed at an inner peripheral edge of the firstsubstrate 91. Therefore, a center cone for fixing an optical disk can beprevented from coming into contact with the second substrate 92 duringuse of the optical disk, and the second substrate 92 can be preventedfrom being damaged or peeled off. In particular, by setting the innerperipheral edge of the second substrate 92 to be larger than a clampregion, only the first substrate 91 is fixed during use of the opticaldisk, and tilt of the optical disk can be prevented. Herein, a “clampregion” refers to a region that is held for rotating an optical diskduring use of the optical disk.

[0130] Furthermore, in the second example, after the second substrate 92is stacked on the first substrate 91, the light 106 is radiated to anouter peripheral side of the clamp region 111, as shown in FIG. 11B,whereby the resin 103 can be prevented from entering the clamp region111. According to this method, the thickness of the clamp region 111 canbe made uniform; as a result, tilt of the optical disk can be reducedfurther.

THIRD EXAMPLE

[0131] In the third example, the case will be described in which onlythe diameter of the central hole 94 h of the protective film 94 isdifferent from that in the second example. The description of the samecomponents as those in the second example will be omitted here.

[0132] In the third example, the diameter of the central hole 92 h isset to be 40 mm, and that of the central hole 94 h is set to be 15 mm.According to this configuration, the same effect as that of the secondexample can be obtained. Furthermore, according to this configuration,the protective film 94 can prevent the resin 103 from adhering to thefirst substrate 91 and the table 101.

FOURTH EXAMPLE

[0133] In the fourth example, the case will be described in which onlythe thicknesses of the second substrate 92 and the protective film 94are different from those in the first example. The description of thesame components as those in the first example will be omitted here.

[0134] In the fourth example, the thickness of the second substrate 92is set to be 90 μm, and the thickness of the protective film 94 is setto be 0.5 mm. In this configuration, the total of the thickness of thesecond substrate 92 and the thickness of the protective film 94 becomesabout 0.6 mm. In the present production of a DVD, two substrates with athickness of 0.6 mm generally are attached to each other. Therefore,according to the configuration of the fourth example, a conventionalproducing apparatus can be used. As described in the second and thirdexamples, the sizes of the central holes 92 h and 94 h may be varied.

FIFTH EXAMPLE

[0135] In the fifth example, the case where the flexural rigidity of theprotective film 94 is varied will be described. The other portions arethe same as those in the first example, so that the repeated descriptionthereof will be omitted here.

[0136] The flexural rigidity of the protective film 94 was varied bychanging the material for the protective film 94. More specifically,optical disks were produced using a protective film with a flexuralrigidity lower than that of the second substrate 92, a protective filmwith the same flexural rigidity as that of the second substrate 92, anda protective film with a flexural rigidity higher than that of thesecond substrate 92. In the fifth example, the thickness of the resin103 was set to be about 20 μm. The optical disks thus obtained weremeasured for a variation in thickness of the resin 103.

[0137] As a result, it was found that in the case where the flexuralrigidity of the protective film 94 is lower than that of the secondsubstrate 92, a variation in thickness of the resin 103 is small. Thereason for this is considered as follows: when the resin 103 is spreadby rotating the table 101, the resin 103 is likely to spread uniformlywhen the flexural rigidity of the protective film 94 is lower.

[0138] On the other hand, when the flexural rigidity of the protectivefilm 94 is higher than that of the second substrate 92, it becomes easyto handle the second substrate 92. Furthermore, even in the case where areflective layer and a signal recording layer are formed on the secondsubstrate 92, they can be formed easily.

[0139] The protective film with a low flexural rigidity and theprotective film with a high flexural rigidity may be formed on thesecond substrate 92. In this case, it is preferable that the protectivefilm with a high flexural rigidity is peeled off before the firstsubstrate 91 and the second substrate 92 are attached to each other, andthe protective film with a low flexural rigidity is peeled off after theattachment.

SIXTH EXAMPLE

[0140] In the sixth example, the case where the second substrate 92 isfixed to the table 101 will be described. The description of the samecomponents as those in the first example will be omitted here.

[0141] First, as shown in FIG. 12A, the second substrate 92 with theprotective film 94 formed on one principal plane is placed on the table101 so that the protective film 94 is placed on the table 101 side.Then, the light-curable resin 103 is dropped onto the second substrate92 through the nozzle 102 so as to be placed in an annual shape. At thistime, the table 101 or the nozzle 102 is rotated at a low speed (20 rpmto 120 rpm). The resin 103 may be applied to the first substrate 91.

[0142] Next, as shown in FIG. 12B, the second substrate 92 is fixed withthe pin 104, and the second substrate 92 is rotated at a high speed(1000 rpm to 12000 rpm) by rotating the table 101. Thus, the excessiveresin 103 is shaken off, whereby a layer of the resin 103 with uniformthickness can be formed on the second substrate 92.

[0143] Next, as shown in FIG. 12C, the first substrate 91 is moved bybeing held by the arm 105, and the central hole of the first substrate91 is fitted on the pin 104. In order to prevent air bubbles from beingmixed between the first substrate 91 and the second substrate 92, thisprocess is conducted in a container 121 under a reduced pressure. It ispreferable that the container 121 is evacuated to 1000 Pa or less.

[0144] The subsequent processes are the same as those in FIGS. 10D and10E, so that the description thereof will be omitted here. Thus, opticaldisks can be produced.

[0145] According to the producing method of Embodiment 2, the substrate10 formed by the producing method of Embodiment 1 may be used as thesecond substrate 92. More specifically, the producing method ofEmbodiment 2 may include the processes (a) and (b) described inEmbodiment 1 prior to the process (A). In this case, an optical disk isproduced using the substrate 11 with the protective layer 12 and theprotective film 94 formed thereon.

[0146] Embodiment 3

[0147] In Embodiment 3, an example of a producing apparatus of thepresent invention used for producing an optical disk will be described.The producing apparatus of Embodiment 3 produces an optical disk using afirst substrate and a second substrate, and is used for conducting theproducing method of Embodiment 2 or 3.

[0148] The producing apparatus of Embodiment 3 includes a firstsubstrate 91, a second substrate 92 with a protective film 94 formed onone principal plane, attachment means for attaching the first substrate91 and the second substrate 92 to each other so that the protective film94 is placed outside, and peeling means for peeling the protective film94. The producing apparatus further may include protective film-formingmeans for forming a protective film on one principal plane of the secondsubstrate.

[0149] As the attachment means, the means described in Embodiment 2 canbe used. The attachment means may include coating means, stacking means,and irradiation means. Furthermore, the attachment means further mayinclude rotation means for rotating the stacked first substrate 91 andsecond substrate 92.

[0150] The coating means is used for coating at least one substrateselected from the group consisting of the first substrate 91 and thesecond substrate 92 with radiation-curable resin. More specifically, thecoating means includes a rotatable table 101, a nozzle 102, a squeegeeand the like.

[0151] The stacking means is used for stacking the first substrate 91and the second substrate 92 on top of the other so that the center ofthe first substrate 91 is matched with that of the second substrate 92.More specifically, the stacking means includes a pin 104, an arm 105 fortransporting a substrate and the like.

[0152] The irradiation means is used for irradiating radiation. Morespecifically, a rare gas lamp such as a xenon lamp, an electron beamsource, a metal halide lamp, a mercury lamp, or the like can be used.

[0153] As the rotation means, a rotatable table can be used.

[0154] Furthermore, the coating means may include dropping means fordropping radiation-curable resin, rotation means for rotating asubstrate onto which radiation-curable resin is dropped and a container121 that can be evacuated. As the dropping means, a nozzle 102 or thelike can be used. Furthermore, as the rotation means, a rotatable table101 or the like can be used. The container 121 that can be evacuatedpreferably can be evacuated to 1000 Pa or less.

[0155] Embodiment 4

[0156] In Embodiment 4, another example of a producing method forproducing an optical disk will be described. The producing method ofEmbodiment 4 is a method for producing an optical disk including asecond substrate with a signal area formed on one principal plane and afirst substrate attached to the second substrate. FIGS. 13A to 13Dschematically show cross-sectional views illustrating the processes of amethod for producing an optical disk of Embodiment 4.

[0157] According to the producing method of Embodiment 4, first, asshown in FIG. 13A, a second substrate 131 with a signal area SA formedon one principal plane 131 a is prepared, and the other principal plane131 b opposite to one principal plane 131 a is fixed to a support 132(Process (i)). The signal area SA may be formed in a later process. Morespecifically, the producing method of Embodiment 4 may include theprocess of forming the signal area SA between the process (i) and theprocess (ii). In this case, the signal area SA can be formed by aphotopolymer method using a stamper or the like. Furthermore, as thesecond substrate 131, for example, the substrate 10 (see FIG. 2B) or thesubstrate 10 a (see FIG. 3B) may be used.

[0158] The second substrate 131 preferably has a thickness in a range of0.03 mm to 0.3 mm, for example, 0.05 mm, 0.1 mm, or 0.2 mm. The secondsubstrate 131 is made of transparent resin such as polycarbonate,acrylic resin, olefin resin, norbornene resin, vinyl ester resin, or thelike. Uneven pits are formed on one principal plane 131 a of the secondsubstrate 131, which function as the signal area SA. More specifically,one principal plane 131 a is a plane onto which an information signal isrecorded. The second substrate 131 is formed by molding resin byinjection molding, casting, extrusion molding, a photopolymer method (2Pmethod), a thermosetting method for curing thermosetting resin withheat, or the like. It is preferable that the second substrate 131 isfixed to the support 132 immediately after being molded. FIG. 14A showsa plan view of the second substrate 131. A shaded area in FIG. 14A isthe signal area SA. FIG. 13 shows the case where a through-hole isformed at the center of the second substrate 131 and the first substrate150 after these substrates are attached to each other. However,substrates having a through-hole may be used as the second substrate andthe first substrate. FIG. 14B shows a plan view of the second substrate131 in this case. As shown in FIG. 14B, the second substrate 131 isprovided with a through-hole 131 h at the center thereof.

[0159] The support 132 is provided with a fixing mechanism (fixingmeans) 133 for fixing the other principal plane 131 b. FIG. 13 shows thecase where the fixing mechanism 133 is placed on one principal plane ofthe support 132. This is shown merely for illustrative purpose, andthere is no particular limit to the configuration of the fixingmechanism 133, as described in the following embodiment. Furthermore,the fixing mechanism also may function as a support. As the method forfixing the other principal plane 131 b to the support 132, at least onemethod selected from the group consisting of a method using staticelectricity, a vacuum adsorption method, a method using a pressuremember, and a method using an adhesive member made of an adhesivematerial can be used. The support 132 and the fixing mechanism 133 areflush with the surface in contact with the second substrate 131, wherebya warp and a wave on the second substrate 131 can be prevented fromoccurring.

[0160] Thereafter, as shown in FIG. 13B, while the second substrate 131is fixed to the support 132, a recording/reflective film 140 includingat least one selected from a metal film, a dielectric film, a magneticfilm and a coloring film is formed on one principal plane 131 a (Process(ii)). The recording/reflective film 140 can be formed by sputtering,vapor deposition or spin coating, depending upon the film to be formed.At this time, the second substrate 131 is fixed to the support 132 bythe above-mentioned fixing method. Therefore, a warp and a wave on thesecond substrate 131 can be prevented from occurring due to the heatgenerated when the recording/reflective film 140 is formed and thestress generated by the recording/reflective film 140.

[0161] Thereafter, as shown in FIG. 13C, the second substrate 131 andthe first substrate 150 are attached to each other with therecording/reflective film 140 interposed therebetween (Process (iii)).The thickness of the first substrate 150 is larger than that of thesecond substrate 131, and is, for example, in a range of 0.5 mm to 1.5mm (e.g., 1.1 mm). The total of the thickness of the second substrate131 and that of the first substrate 150 preferably is in a range of 0.5mm to 0.7 mm, or in a range of 1.1 mm to 1.3 mm.

[0162] The first substrate 150 may have a signal area (signal surface)on the side that is to be attached to the second substrate 131. Examplesof the method for attaching the second substrate 131 and the firstsubstrate 150 to each other include a method (see FIG. 13C) usingradiation-curable resin 151, a hot-melt method and a method using anadhesive sheet. In the case of using the radiation-curable resin,specifically, the radiation-curable resin 151 is applied between thesecond substrate 131 and the first substrate 150, and the secondsubstrate 131 and the first substrate 150 are stacked on top of theother. Thereafter, two stacked substrates are spun to spread theradiation-curable resin 151, and then, the radiation 152 is radiated,whereby the radiation-curable resin 151 may be cured. As theradiation-curable resin, for example, UV-curable resin, resin that iscured by irradiation with an electron beam or the like can be used. InFIG. 13C, radiation is radiated from the first substrate 150 side.However, radiation may be radiated from the support 132 side, using asubstrate and a support made of a radiation-transmitting material forthe second substrate 131 and the support 132. Because of this, even inthe case where the recording/reflective film having no radiationpermeability is formed on the first substrate 150, the radiation-curableresin placed between the second substrate 131 and the first substrate150 can be cured easily.

[0163] Thereafter, as shown in FIG. 13D, the other principal plane 131 bof the second substrate 131 is released from the support 132 (Process(iv)). Thus, an optical disk 130 is obtained in which the secondsubstrate 131 and the first substrate 150 are attached to each otherwith the recording/reflective film 140 interposed therebetween.

[0164] In the case where the second substrate 131 has a circularthrough-hole 131 h at the center (see FIG. 14B), the other principalplane 131 b can be fixed to the support 132 by pressing at least oneselected from an inner peripheral edge 131 s and an outer peripheraledge 131 t of the second substrate 131 to the support 132, using apressure member. In this case, it is preferable that the other principalplane 131 b is fixed to the support 132 by a method different from theabove-mentioned pressure member prior to the process (iii) after theprocess (ii), whereby pressing with the pressure member is finished. Asthe above-mentioned different method, at least one selected from amethod using vacuum adsorption and a method using static electricity canbe used. The method for fixing the other principal plane 131 b to thesupport 132 will be described specifically in the following embodiment.

[0165] According to the producing method of Embodiment 4, after thesecond substrate 131 is fixed to the support 132, therecording/reflective film 140 is formed. Therefore, according to theproducing method of Embodiment 4, even in the case where the secondsubstrate 131 is thin, a warp and a wave can be prevented from occurringon the second substrate 131, and the second substrate 131 becomes likelyto be handled. Therefore, according to the method for producing anoptical disk of Embodiment 4, an optical disk with less warp and wavecan be produced easily.

[0166] Embodiment 5

[0167] In Embodiment 5, an example of an apparatus for producing anoptical disk of the present invention will be described, which can beused for the method for producing an optical disk of the presentinvention described in Embodiment 4. The same components as those inEmbodiment 4 are denoted with the same reference numerals as thosetherein, and repeated description thereof will be omitted here. FIG. 15schematically shows the configuration of an optical disk producingapparatus 200 of Embodiment 5. In the following figures, hatching may beomitted for ease of understanding.

[0168] The optical disk producing apparatus 200 includes a substratesupply device 210, substrate transporting devices 220, 240 and 260, afilm-forming device 230, a substrate attaching device 250 and an opticaldisk recovery device 270. The optical disk producing apparatus 200 alsoincludes supports 132 transported from the substrate supply device 210to the optical disk recovery device 270.

[0169] The substrate supply device 210 successively transfers the secondsubstrate 131 to a plurality of supports 132 in the substratetransporting device 220. The substrate supply device 210 is suppliedwith the second substrate 131 from a substrate producing device (notshown) such as an injection molder or a 2P producing device.

[0170] The substrate transporting device 220 is placed so as to move thesupport 132, to which the second substrate 131 is fixed, from thesubstrate supply device 210 to the film-forming device 230. Similarly,the substrate transporting device 240 is placed so as to move thesupport 132, to which the second substrate 131 is fixed, from thefilm-forming device 230 to the substrate attaching device 250, and thesubstrate transporting device 260 is placed so as to move the support132, to which the second substrate 131 is fixed, from the substrateattaching device 250 to the optical disk recovery device 270.

[0171] As shown in FIG. 15, the substrate transporting devices 220 and260 have a plurality of supports 132 for fixing the second substrates131, driving mechanisms 221 for transporting the supports 132, andsupport moving devices 222. The optical disk producing apparatus 200includes fixing mechanisms (fixing means) 133 for fixing the otherprincipal plane 131 b on the opposite side of the signal area of thesecond substrate 131 to the support 132. The support moving device 222has a function of receiving the support 132, to which the secondsubstrate 131 is fixed, from the device in the previous process of thesubstrate transporting devices 220, 240 and 260, and transferring themto the device in the subsequent process. Although not shown, thesubstrate transporting device 240 also has the same function.

[0172] The film-forming device 230 functions as means for forming therecording/reflective film 140. That is, the optical disk producingapparatus 200 includes film-forming means for forming a film includingat least one selected from a metal film, a dielectric film, a magneticfilm and a coloring film. More specifically, as the film-forming device230, a device including at least one selected from a sputtering device,a vacuum film-forming device such as a vapor deposition device and aspin coater can be used.

[0173] In the case of attaching the second substrate 131 and the firstsubstrate 150 to each other, using radiation-curable resin, thesubstrate attaching device 250 functions as means for attachingsubstrates, and includes, for example, a coating device for applyingradiation-curable resin between the second substrate 131 and the firstsubstrate 150 fixed on the support 132 and means for irradiatingradiation that cures radiation-curable resin. As the coating device, aspinner provided with a resin dropping nozzle, a screen printing deviceand the like can be used. As the irradiation means, a mercury lamp, ametal halide lamp, a rare gas lamp or the like can be used.

[0174] In the substrate transporting device 260, by releasing the otherprincipal plane 131 b of the second substrate 131 from the fixingmechanism 133, the optical disk 130, in which the second substrate 131and the first substrate 150 are integrated, is released and transferredto the disk recovery device 270. In the disk recovery device 270, theoptical disks 130 are stacked on a stock pole for recovery (not shown).

[0175] As the method for fixing the other principal plane 131 b of thesecond substrate 131 to the support 132, various methods can be used.More specifically, at least one method selected from a method usingstatic electricity, a method using vacuum adsorption, a method using apressure member and a method using an adhesive member made of anadhesive material can be used. In this case, the optical disk producingapparatus 200 includes a static electricity generating device, a vacuumadsorption device, a pressure member, an adhesive member formed on asupport and the like, in accordance with the respective methods.

[0176] The case where the second substrate 131 is fixed to the support132 using static electricity will be described with reference to FIGS.16A and 16B.

[0177]FIG. 16A shows a method in the case of fixing the second substrate131 and the support 132 to each other by supplying a charge to thesecond substrate 131. In this case, an insulator is used for the support132. According to this method, first, the second substrate 131 is placedon a base 282 made of an insulator. Then, a negative charge supplydevice 280 is connected to a part of the second substrate 131, andnegative charge 281 is supplied to the inside of the second substrate131 by the negative charge supply device 280. Since the base 282 is aninsulator, the negative charge 281 is accumulated in the secondsubstrate 131 without moving to the base 282. After the elapse of apredetermined period of time, the negative charge supply device 280 isdisconnected from the second substrate 131, and the second substrate 131is placed on the insulating support 132 shown in FIG. 16B.

[0178] The material for the support 132 is an insulator such as ceramic.In the support 132, an electrode 283 and charged bodies such as lithiumniobate placed on the electrode 283 are buried. A part of the chargedbodies 284 is exposed to a surface 132 a side of the support 132 that isin contact with the second substrate 131. The electrode 283 is connectedto a power source 290 for applying a voltage via a connection pin 286 ata connecting portion 285.

[0179] The power source 290 for applying a voltage includes a powersource 291 for supplying a charge, a ground terminal 292 and a switch293 so that charge is supplied to the electrode 283. In the firstsupport 132 on the substrate transporting device 220 shown in FIG. 15,the connection pin 286 is inserted into the support 132 and connected tothe connecting portion 285.

[0180] Next, the switch 293 is switched to the power source 291 forsupplying a charge, and positive charge is supplied from the powersource 291 for supplying a charge to the electrode 283. At this time,negative charge is generated on the surface of the charged body 284 thatis in contact with the electrode 283 due to polarization, andsimultaneously, positive charge is generated on the surface 132 a sideof the charged body 284. The positive charge and the negative chargeaccumulated in the second substrate 131 by the negative charge supplydevice 280 attract each other; as a result, a part of the secondsubstrate 131 is fixed to the charged body 284, that is, the support132. Thereafter, the connection pin 286 is disconnected from theconnecting portion 285, and the support 132 to which the secondsubstrate 131 is fixed is transported by the driving mechanism 221successively.

[0181] After the first substrate 150 and the second substrate 131 areattached to each other by the substrate attaching device 250, in orderto release the optical disk 130 from the support 132, the switch 293 inthe power source 290 for applying a voltage is switched to the groundterminal 292 in the substrate transporting device 260, and theconnection pin 286 is connected to the connecting portion 285 again.Simultaneously with the connection, the positive charge in the electrode283 moves to the ground through the ground terminal 292, andpolarization in the charged body 284 is finished. Consequently, theother principal plane 131 b of the second substrate 131 is released fromthe support 132. Thus, the optical disk 130 is released.

[0182] As described above, according to the method for fixing the secondsubstrate 131 using static electricity, the optical disk producingapparatus 200 includes, as means for fixing the second substrate 131, astatic electricity generating device including the negative chargesupply device 280, the electrode 283 and the charged bodies 284 buriedin the support 132 and the power source 290 for applying a voltage.According to this method, the charged bodies 284 in the support 132 arecharged or discharged under the condition that the second substrate 131is charged, whereby the second substrate 131 can be fixed onto thesupport 132 or released therefrom with ease.

[0183] It is preferable that the exposed surfaces of the charged bodies284 are flat and have no step with respect to the surface 132 a of thesupport 132. Because of this, when the second substrate 131 is fixed tothe support 132, the second substrate 131 can be prevented from beingdeformed locally. If the second substrate 131 having a local deformationis fixed to the support 132 and attached to the first substrate 150, thecompleted optical disk 130 also has a similar local deformation.Furthermore, it is preferable that the pattern of exposed portions ofthe charged bodies 284 seen from the surface 132 a side is in aconcentric shape whose central axis is equal to that of the support 132.If the exposed portions have a concentric pattern, when the secondsubstrate 131 is fixed, the second substrate 131 can be prevented frombeing deformed locally in a track direction.

[0184] Furthermore, it is preferable that the shape of the surface 132 ain a radius direction should be selected so that the warp of thecompleted optical disk 130 becomes minimum (this also applies to thefollowing embodiment). For example, if it is assumed that, in theattachment process, the optical disk 130 is likely to have a shape inwhich the second substrate 131 side is dented due to curingcharacteristics of an attachment material such as UV-curable resin, itis preferable to prescribe the cross-sectional shape of the surface 132a to be as shown in FIG. 17A. This allows the shape of the completedoptical disk to be flat. In contrast, assuming that the completedoptical disk 130 is likely to have a shape in which the first substrate150 side is dented, if the shape of the surface 132 a in a radiusdirection is prescribed to be as shown in FIG. 17B, the shape of thecompleted optical disk 130 can be made flat.

[0185] In the optical disk producing apparatus of Embodiment 5, anoptical disk can be produced easily in accordance with the method forproducing an optical disk described in Embodiment 4. Therefore,according to the optical disk producing apparatus of Embodiment 5, anoptical disk without any warp and wave can be produced easily.

[0186] In Embodiment 5, the case where the concentric charged bodies 284are buried in the support 132 has been described. However, the chargedbodies 284 are not necessarily in a concentric shape. For example, thecharged bodies 284 may be exposed over the entire surface that is incontact with the second substrate 131.

[0187] Furthermore, in Embodiment 5, the case where the substrates areattached to each other using radiation-curable resin has been described.However, it also may be possible to use an apparatus for attachingsubstrates with a hot-melt material, an apparatus for attachingsubstrates with a slow-acting material that is cured gradually after anelapse of time triggered by irradiation with UV-light, or an apparatusfor attaching substrates with a film made of an adhesive material (thisalso applies to the following embodiment).

[0188] Furthermore, in Embodiment 5, the case where a circularthrough-hole is not formed at the center of the second substrate 131 hasbeen described. It is appreciated that a circular through-hole may beformed at the center of the second substrate 131.

[0189] Furthermore, as described in Embodiment 6, it also is appreciatedthat the first substrate 150 may have a signal area.

[0190] Furthermore, the producing apparatus of Embodiment 5 further mayinclude means for forming a signal area (this also applies to theapparatus of Embodiment 6). According to this configuration, after thesecond substrate without a signal area SA is fixed to the support, asignal area can be formed on the second substrate. An example of meansfor forming a signal area includes an apparatus (2P unit) for conductinga photopolymer method. The 2P unit includes, for example, a coatingdevice for coating the second substrate with photopolymer resin, and atransfer device for transferring the pattern of a mask. As the coatingdevice, a nozzle, a screen printing device (screen and spatula), aroller or the like can be used. Furthermore, as the transfer device, amaster with a predetermined pattern formed thereon, a UV irradiationdevice, and a unit for peeling the master off the second substrate afterirradiation with UV-light.

[0191] Embodiment 6

[0192] In Embodiment 6, another example of an optical disk producingapparatus of the present invention will be described. The optical diskproducing apparatus of Embodiment 6 is different from that described inEmbodiment 5 only in the fixing means (fixing mechanism) of the secondsubstrate 131. Therefore, repeated description of the same portions asthose described in the above embodiment may be omitted

[0193] In Embodiment 6, the case where the second substrate 131 has acircular through-hole 131 h (see FIG. 14B) at the center will beexemplified. Furthermore, in Embodiment 6, a single-sided two-layeroptical disk will be exemplified, in which a first substrate also has asignal area on the surface of the second substrate side, and informationcan be recorded and reproduced with respect to a recording layer on thesecond substrate and a recording layer on the first substrate byirradiation with laser light from the second substrate side.

[0194] The optical disk producing apparatus of Embodiment 6 includes, asfixing means for fixing the other principal plane 131 b of the secondsubstrate 131 to the support 132, pressure means for pressing at leastone selected from the inner peripheral edge 131 s and the outerperipheral edge 131 t (see FIG. 14B) of the second substrate 131 to thesupport 132 side. It is preferable that the optical disk producingapparatus of Embodiment 6 includes, as fixing means for fixing the otherprincipal plane 131 b to the support 132, second fixing means differentfrom the pressure means. As the second fixing means, for example, atleast one selected from a vacuum adsorption device and a staticelectricity generating device can be used.

[0195]FIGS. 18A and 18B show a fixing mechanism of the second substrate131 in the optical disk producing apparatus of Embodiment 6.

[0196] As shown in FIG. 18A, the second substrate 131 (thickness ispreferably 0.3 mm or less (e.g., 0.05 mm, 0.1 mm or 0.2 mm) is fixed bypressing the inner peripheral edge 131 s onto a support 320 from oneprincipal plane (signal plane) 131 a side by an inner periphery pressuremember 300 and by pressing the outer peripheral edge 131 t to thesupport 320 from one principal plane (signal plane) 131 a side by anouter periphery pressure member 310.

[0197] The inner periphery pressure member 300 includes a circular diskportion and a columnar portion 302 connected to the disk portion 301.The disk portion 301 has a diameter larger than that of a circularthrough-hole 131 h positioned at the center of the second substrate 131,which does not reach the signal area SA. Furthermore, the columnarportion 302 has a size that can be inserted into the through-hole 131 h.The columnar portion 302 is inserted into the through-hole 131 h, and isinserted into a hole provided at the center of the support 320.

[0198] The outer periphery pressure member 310 has a shape in which aflat plate ring with a large inner diameter and a flat plate with asmall inner diameter are attached to each other concentrically. A smallinner diameter “d_(i)” of the outer periphery pressure member 310 issmaller than an outer diameter of the second substrate 131. Furthermore,a large inner diameter “d_(o)” of the outer periphery pressure member310 is larger than the outer diameter of the second substrate 131.

[0199] The inner periphery pressure member 300 and the outer peripherypressure member 310 are made of a magnetic substance, and stainlesssteel can be used, for example. Permanent magnets 330 are attached toportions of the support 320 that the inner periphery pressure member 300and the outer periphery pressure member 310 are in contact with, and thepermanent magnets 330 fix the inner periphery pressure member 300 andthe outer periphery pressure member 310 made of a magnetic substance tothe support 320. More specifically, the optical disk producing apparatusof Embodiment 6 includes, as fixing means for fixing the other principalplane 131 b of the second substrate 131 to the support 320, the innerperiphery pressure member 300, the outer periphery pressure member 310and the permanent magnets 330, and fixes the other principal plane 131 bto the support 320 by using a magnetic force. Electromagnets may be usedin place of the permanent magnets.

[0200] The disk portion 301 of the inner periphery pressure member 300and the outer periphery pressure member 310 can be used not only as thefixing means for fixing the second substrate 131 to the support 320, butalso as a mask during formation of a recording/reflective film. In thiscase, a mask is not required for the film-forming device 230. Generally,in production of an optical disk, a recording/reflective film also isdeposited onto a mask, so that it is required to replace a mask in achamber of the film-forming device 230 regularly. However, in this case,the chamber is exposed to the atmosphere every time the mask isreplaced, which requires evacuation of the chamber after the mask isreplaced, resulting in a decrease in productivity. However, if the innerperiphery pressure member 300 and the outer periphery pressure member310 are used as a mask as described above, the mask can be replacedeasily outside of the chamber, and a down time for exposure to theatmosphere and evacuation of the chamber can be shortened, which canenhance productivity.

[0201] The support 320 includes a plurality of aspiration holes 340, andthe aspiration holes 340 are connected to a discharge device 350, suchas a vacuum pump, through a tube. More specifically, the optical diskproducing apparatus of Embodiment 6 includes, as fixing means,aspiration holes 340 formed in the support 320 and the discharge device350, in addition to the pressure means. In the optical disk producingapparatus of Embodiment 6, it is required that the inner peripherypressure member 300 and the outer periphery pressure member 310 areremoved so as to attach the second substrate 131 and the first substrate150 to each other after the second substrate 131 is fixed by the innerperiphery pressure member 300 and the outer periphery pressure member310, and a recording/reflective film is formed on a signal area SA bythe film-forming device 230. In this case, if the second substrate 131is held under vacuum through the aspiration holes 340 before the innerperiphery pressure member 300 and the outer periphery pressure member310 are removed, and the inner periphery pressure member 300 and theouter periphery pressure member 310 are removed under the condition thatthe second substrate 131 is fixed to the support 320, a warp and a waveof the second substrate 131 can be suppressed. The vacuum adsorptiondevice also can be used for fixing the second substrate 131 togetherwith the pressure member, in the case where the second substrate 131 isnot fixed sufficiently by the inner periphery pressure member 300 andthe outer periphery pressure member 310.

[0202] In the optical disk producing apparatus of Embodiment 6, it ispreferable that the support 320 is made of a material havingUV-permeability such as quartz glass, and a UV-light irradiation lamp isprovided below the support 320 (on the side opposite to the secondsubstrate 131 with respect to the support 320). According to thisconfiguration, even in the case of using the first substrate 150including a recording/reflective film substantially having noUV-permeability as a signal layer, UV-light is radiated from the support320 side, whereby UV-curable resin placed between the second substrate131 and the first substrate 150 can be cured. FIG. 18B shows the processat this time.

[0203] As shown in FIG. 18B, the second substrate 131 with the innerperiphery pressure member 300 and the outer periphery pressure member310 removed therefrom is fixed to the support 320 by vacuum adsorptionusing the aspiration holes 340. By irradiating the radiation 152 such asUV-light from the support 320 side, the radiation-curable resin 151placed between the second substrate 131 and the first substrate 150 iscured. The radiation 152 is radiated from a radiation irradiation device(irradiation means) 341 such as a mercury lamp, a metal halide lamp, anda rare gas lamp.

[0204] Thus, in the optical disk producing apparatus of Embodiment 6, asingle-sided two-layer optical disk can be produced easily in which thesecond substrate 131 and the first substrate 150 are integrated witheach other.

[0205]FIGS. 19A and 19B schematically show a configuration of a pressuremember transport arm 400 for fixing and releasing the second substrate131, using the inner periphery pressure member 300 and the outerperiphery pressure member 310. The pressure member transport arm 400includes air cylinders 410 and permanent magnets 420 fixed to shafts ofthe air cylinders 410. The magnetic force of the permanent magnets 420is stronger than that of the permanent magnets 330 on the support 320.

[0206] When the inner periphery pressure member 300 and the outerperiphery pressure member 310 are removed from the support 320, theshafts of the air cylinders 410 move downward (in the direction wherethe inner periphery pressure member 300 and the outer periphery pressuremember 310 are placed), and the permanent magnets 420 approach the innerperiphery pressure member 300 and the outer periphery pressure member310. The magnetic force of the permanent magnets 420 is stronger thanthat of the permanent magnets 330, so that the inner periphery pressuremember 300 and the outer periphery pressure member 310 are removed fromthe support 320, and held by the pressure member transport arm 400 (seeFIG. 19A).

[0207] In contrast, when the inner periphery pressure member 300 and theouter periphery pressure member 310 are transferred from the pressuremember transport arm 400 to the support 320, the shaft of the aircylinder 410 moves upward (in the direction opposite to the directionwhere the inner periphery pressure member 300 and the outer peripherypressure member 310 are placed). Therefore, the permanent magnets 420move away from the inner periphery pressure member 300 and the outerperiphery pressure member 310 (see FIG. 19B). As a result, the innerperiphery pressure member 300 and the outer periphery pressure member310 are fixed to the support 320 by a magnetic force of the permanentmagnets 330 on the support.

[0208] As described above, in Embodiment 6, an optical disk producingapparatus and a method using the same have been described, in which apressure member is used as a method for fixing the second substrate tothe support before formation of a recording/reflective film, and thepressure member is moved between the support and the pressure membertransport arm by permanent magnets. However, according to the opticaldisk producing method and apparatus of the present invention, as amethod for fixing a pressure member to a support or a pressure membertransport arm, a method and mechanism may be used in which holes forvacuum adsorption are provided on the surface in contact with thesupport and the pressure member of the pressure member transport arm,and the pressure member is fixed to the support and the pressure membertransport arm by vacuum adsorption.

[0209] Furthermore, as a method for fixing the second substrate to thesupport before the pressure member is removed from the support afterformation of a recording/reflective film, a method and mechanism may beused in which a charged substance is provided on the support, and thesecond substrate is fixed to the support by static electricity of thecharged substance.

[0210] According to the optical disk producing apparatus of Embodiment6, an optical disk can be produced by the method for producing anoptical disk described in Embodiment 4. Therefore, an optical diskwithout any warp and wave can be produced easily.

[0211] The invention may be embodied in other forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not limiting. The scope of the invention is indicatedby the appended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

[0212] Industrial Applicability

[0213] As described above, according to the method for producing adisk-shaped substrate of the present invention, it is possible toproduce a disk-shaped substrate whose surface is unlikely to be damagedand which can be handled easily. The disk-shaped substrate can be usedfor producing an optical disk obtained by attaching two substrates.

[0214] Furthermore, according to the first and second producing methodsof the present invention for producing an optical disk, an optical diskcan be produced easily in which the surface of a substrate on alight-incident side is unlikely to be damaged.

[0215] Furthermore, according to the first and second producingapparatus for producing an optical disk, the first and second productionmethods of the present invention can be conducted easily.

1. (Amended) A method for producing a disk-shaped substrate used forproducing an optical disk, comprising the processes of: (a) forming aprotective layer that is larger in area than the disk-shaped substrateon a surface of a transparent plate having a thickness in a range of0.03 mm to 0.3 mm; and (b) cutting a portion of the plate with theprotective layer formed thereon other than an outer edge portion of theprotective layer to form a disk shape.
 2. (Cancelled)
 3. A method forproducing a disk-shaped substrate according to claim 1, wherein theprotective layer is made of radiation-curable resin.
 4. A method forproducing a disk-shaped substrate according to claim 3, wherein theplate has a disk shape with a diameter larger than that of thedisk-shaped substrate.
 5. A method for producing a disk-shaped substrateaccording to claim 4, wherein the process (a) includes coating the platewith the radiation-curable resin by spin coating, and curing theradiation-curable resin.
 6. A method for producing a disk-shapedsubstrate according to claim 1, wherein the protective layer is made ofa material with a hardness higher than that of the plate.
 7. A methodfor producing a disk-shaped substrate according to claim 1, wherein theprotective layer is made of a material with a coefficient of frictionsmaller than that of the plate.
 8. A method for producing a disk-shapedsubstrate according to claim 1, wherein the protective layer is made ofan inorganic substance, and the protective layer is formed by chemicalvapor deposition in the process (a).
 9. A method for producing adisk-shaped substrate according to claim 1, wherein the process (a)further includes forming an inorganic layer made of an inorganicsubstance on the protective layer.
 10. (Cancelled)
 11. (Cancelled) 12.(Cancelled)
 13. (Cancelled)
 14. (Cancelled)
 15. (Cancelled) 16.(Cancelled)
 17. (Cancelled)
 18. (Cancelled)
 19. (Cancelled) 20.(Cancelled)
 21. (Cancelled)
 22. (Cancelled)
 23. (Cancelled) 24.(Cancelled)
 25. (Cancelled)
 26. A method for producing an optical diskincluding a first substrate and a second substrate in which a signalarea is to be formed on one principal plane, comprising the processesof: (i) fixing the other principal plane of the second substrate, whichis an opposite side of the one principal plane, to a support; (ii)forming at least one film selected from a metal film, a dielectric film,a magnetic film and a coloring film on the one principal plane; (iii)attaching the first substrate and the second substrate to each otherwith the at least one film interposed therebetween; and (iv) releasingthe other principal plane of the second substrate from the support. 27.A method for producing an optical disk according to claim 26, wherein athickness of the second substrate is in a range of 0.03 mm to 0.3 mm.28. A method for producing an optical disk according to claim 26,wherein the first substrate includes a signal area on one principalplane on a side that is attached to the second substrate.
 29. A methodfor producing an optical disk according to claim 26, wherein the firstsubstrate and the second substrate are attached to each other usingradiation-curable resin in the process (iii).
 30. A method for producingan optical disk according to claim 29, wherein the support and thesecond substrate have radiation permeability, and the first substrateand the second substrate are attached to each other by curing theradiation-curable resin by radiation from the support side in theprocess (iii).
 31. A method for producing an optical disk according toclaim 26, comprising forming the signal area on the one principal planeof the second substrate after the process (i) and before the process(ii).
 32. A method for producing an optical disk according to claim 26,wherein the second substrate has a circular through-hole at a centerthereof, and the process (i) includes pressing at least one selectedfrom an inner peripheral edge and an outer peripheral edge of the secondsubstrate to the support side by a pressure member, thereby fixing theother principal plane to the support.
 33. An apparatus for producing anoptical disk using a first substrate and a second substrate, comprising:attachment means for attaching the first substrate and the secondsubstrate with a protective film formed on one principal plane to eachother so that the protective film is placed outside; and peeling meansfor peeling the protective film.
 34. An apparatus for producing anoptical disk according to claim 33, further comprising film-formingmeans for forming the protective film on the one principal plane of thesecond substrate.
 35. An apparatus for producing an optical diskaccording to claim 33, wherein the attachment means includes: coatingmeans for coating at least one substrate selected from the firstsubstrate and the second substrate with radiation-curable resin;stacking means for stacking the first substrate and the second substrateso that a center of the first substrate is matched with a center of thesecond substrate; and irradiation means for irradiating theradiation-curable resin with radiation.
 36. An apparatus for producingan optical disk according to claim 35, wherein the attachment meansfurther includes rotation means for rotating the stacked first substrateand second substrate.
 37. An apparatus for producing an optical diskaccording to claim 35, wherein the coating means includes dropping meansfor dropping the radiation-curable resin onto the at least one substrateand rotation means for rotating the at least one substrate, and thestacking means includes a container that can be evacuated.
 38. Anapparatus for producing an optical disk including a first substrate anda second substrate in which a signal area is to be formed on oneprincipal plane, comprising: a support for supporting the otherprincipal plane of the second substrate, which is an opposite side ofthe one principal plane; and fixing means for fixing the other principalplane to the support.
 39. An optical disk producing apparatus accordingto claim 38, further comprising film-forming means for forming at leastone film selected from a metal film, a dielectric film, a magnetic filmand a coloring film on the one principal plane.
 40. An optical diskproducing apparatus according to claim 38, further comprising attachmentmeans for attaching the first substrate and the second substrate to eachother.
 41. An optical disk producing apparatus according to claim 40,wherein the support is made of a radiation-permeable material, and theattachment means includes irradiation means on a side opposite to a sidewhere the second substrate is placed with respect to the support.
 42. Anoptical disk producing apparatus according to claim 38, wherein thesecond substrate has a circular through-hole at a center thereof, andthe fixing means includes pressure means for pressing at least oneselected from an inner peripheral edge and an outer peripheral edge ofthe second substrate to the support side.
 43. An optical disk producingapparatus according to claim 38, further comprising signal area formingmeans for forming the signal area on the one principal plane of thesecond substrate.